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<div  id='write'  class = 'is-node'><h1><a name="10-java%E5%A4%9A%E7%BA%BF%E7%A8%8B" class="md-header-anchor"></a><span>10 Java多线程</span></h1><ul><li><a href='http://wiki.jikexueyuan.com/project/java-concurrency/'><span>Java并发编程</span></a></li></ul><h2><a name="synchronized" class="md-header-anchor"></a><span>synchronized</span></h2><p><span>synchronized 可以用来修饰方法、静态方法、代码块。</span><br/><span>可以保证代码的原子性与可见性。</span><br/><strong><span>原子性</span></strong><span>：原子性就是不可分割，代码块在执行时，CPU不能中断当前线程切换到其他线程。</span><br/><strong><span>可见性</span></strong><span>：操作执行完毕后立刻将改变的变量值刷新到主内存，保证其他线程获取到的都是最新的值。</span></p><blockquote><p><span>volatile 关键字用于修饰变量，只能保证可见性，因此 synchronized 关键字为首选。</span></p></blockquote><p><span>当一个线程访问 synchronized 修饰的代码前必须获得锁，否则改线程会一直等待，代码退出或抛出异常后必然会释放锁。</span></p><p><span>方法和代码块的锁即为该方法或代码块所属对象。也就是同一个对象中的多个不同 synchronized 修饰的方法和代码块的锁是相同的，一条线程在访问其中一个 synchronized 方法时，其他线程不能访问该独享的其他 synchronized 方法。</span></p><p><span>静态方法的锁是当前对象的 Class 对象（所有同一个类的对象的 Class 对象都是同一个），所以含有静态 synchronized  方法和普通 synchronized  方法的对象中的这两种方法的锁是不同的，这两种方法可以同时被两个线程访问。</span></p><p><span>Java 的 synchronized 块是可重入的，可重入的意思是线程可以重复获得它已经持有的锁，这样一来，相同锁的方法可以互相调用，而不会发生死锁。</span></p><pre spellcheck="false" class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 30px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 26px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><span><span>​</span>x</span></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -26px; width: 26px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -26px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 18px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-comment">//synchronized 代码块，这里的 this 应该是指该代码块的锁是当前对象</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -26px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 18px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">synchronized</span> (<span class="cm-keyword">this</span>){</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -26px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 18px;">3</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="">​</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -26px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 18px;">4</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 80px;"></div><div class="CodeMirror-gutters" style="height: 80px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 26px;"></div></div></div></div></pre><pre spellcheck="false" class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 34px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>10</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -34px; width: 34px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-comment">//这里 outer 方法调用 inner 方法时，由于可重入，所以不需要等待 outer 方法释放锁</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-comment">//如果不可重入，那 outer 方法在执行 inner 方法时会一直等待自身释放锁，但那是不可能的，于是陷入死锁</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">3</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Reentrant</span>{</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">4</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; <span class="cm-keyword">public</span> <span class="cm-keyword">synchronized</span> <span class="cm-variable">outer</span>(){</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">5</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; <span class="cm-variable">inner</span>();</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">6</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; }</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">7</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; <span class="cm-keyword">public</span> <span class="cm-keyword">synchronized</span> <span class="cm-variable">inner</span>(){</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">8</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; <span class="cm-comment">//do something</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">9</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; }</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">10</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 200px;"></div><div class="CodeMirror-gutters" style="height: 200px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 34px;"></div></div></div></div></pre><blockquote><p><code>Thlead.sleep()</code><span>不会释放锁，在编写示例程序时可以使用这个方法，避免程序运行太快，看不出并发效果。</span></p></blockquote><h2><a name="%E7%BA%BF%E7%A8%8B%E9%97%B4%E9%80%9A%E4%BF%A1%EF%BC%8Cwait%E3%80%81notify%E3%80%81notifyall" class="md-header-anchor"></a><span>线程间通信，wait、notify、notifyAll</span></h2><p><span>这三个方法必须在同步块或同步方法中调用。</span><br/><span>通信的原理是多个线程都需要访问同一个对象时，该对象内部通过调用这三个方法来使线程等待或唤醒线程。</span><br/><span>对象拥有线等待池和锁池、访问对象的线程可以在等待池中等待（对象调用 wait 方法），在锁池中竞争锁（对象调用 notify 方法）或者在获得锁后执行。</span></p><p><span>notify会唤醒所有在该对象等待池中的线程，而notify只会随机唤醒一个。优先级高的线程有更大的可能竞争到锁，而不是有更大的可能被唤醒。</span></p><p><code>wait(long millis)</code><span>可以使线程在超过一定时间后自动唤醒，而不需要 notify 方法。</span><br/><strong><span>wait 方法和 Thread.sleep 方法最大的不同是 wait 会释放锁</span></strong><span>。</span></p><h3><a name="%E9%80%9A%E7%9F%A5%E9%81%97%E6%BC%8F%E9%97%AE%E9%A2%98%EF%BC%8C%E6%97%A9%E6%9C%9F%E9%80%9A%E7%9F%A5%E9%97%AE%E9%A2%98" class="md-header-anchor"></a><span>通知遗漏问题，早期通知问题</span></h3><p><span>所谓通知遗漏就是当线程 A 还没有 wait 的时候，线程 B 已经使用了 notify 方法，这样当线程 A wait 后便没有线程来唤醒它了，那它将一直等待。</span></p><p><span>所谓早期通知问题就是线程被 notify 方法唤醒，但其实该线程还有等待的其他条件没被满足。比如线程需要从 list 中取出一个对象，某个时间点它被唤醒，但此时 list 为空，无法取出对象。</span></p><p><span>以下是解决通知遗漏问题和早期通知问题后的代码示例。</span></p><p><span>通知遗漏问题（需要在方法A中加入sleep来保证方法B先被执行）。</span><br/><span>main 方法中启动两条线程，一条执行方法 A，一条执行方法 B。</span><br/><span>正确的顺序应该是，线程 A 等待添加产品 -- 线程 B 添加产品 -- 线程 A取出产品。</span><br/><span>如果线程 B 先添加产品、那线程 A 将一直等待添加产品，它并不知道产品已被添加。</span><br/><strong><span>所以线程A在等待前要判断是否真的需要等待，比如生产者消费者模型，消费者要在当前产品数为0的情况下才wait</span></strong><span>。</span></p><p><span>早期通知问题（需要在方法B中添加sleep来保证方法A先被执行）。</span><br/><span>main 中启动两条消费者线程都执行方法A，再启动一条生产者线程来执行方法B。</span><br/><span>开始时有</span><strong><span>两条消费者线程</span></strong><span>在等待产品添加，之后生产者线程添加产品后，其中一条消费者线程被唤醒，取出产品（现在已经没有产品了），接着另一条消费者线程被唤醒，该线程没有产品可取，所以它应该继续等待。</span><br/><strong><span>消费者线程在被唤醒后，先判断是否有产品，有就消费，没有就继续等待</span></strong><span>。  </span></p><p><span>方法是在 wait 外面包裹 while 循环，如果仅仅是针对通知遗漏问题，那 wait 外面包裹 if 判断也没什么问题。</span></p><pre spellcheck="false" class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 34px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>21</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -34px; width: 34px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">ThreadNotify</span> {</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-keyword">private</span> <span class="cm-variable-3">boolean</span> <span class="cm-variable">isEmpty</span> <span class="cm-operator">=</span> <span class="cm-atom">true</span>;</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">3</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">methodA</span>() <span class="cm-keyword">throws</span> <span class="cm-variable">InterruptedException</span> {</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">4</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-keyword">synchronized</span> (<span class="cm-keyword">this</span>) {</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">5</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"方法A：等待添加产品"</span>);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">6</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-comment">// 用一个 boolean 变量来判断当前是否有产品被添加，没有就等待</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">7</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-keyword">while</span>(<span class="cm-variable">isEmpty</span>)</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">8</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-variable">wait</span>();</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">9</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"方法A：取出产品"</span>);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">10</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-variable">isEmpty</span> <span class="cm-operator">=</span> <span class="cm-atom">true</span>;</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">11</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp;  }</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">12</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp;  }</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">13</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text="">​</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">14</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">methodB</span>(){</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">15</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-keyword">synchronized</span> (<span class="cm-keyword">this</span>) {</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">16</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"方法B：添加产品"</span>);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">17</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-variable">isEmpty</span> <span class="cm-operator">=</span> <span class="cm-atom">false</span>;</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">18</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-variable">notify</span>();</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">19</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp;  }</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">20</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp;  }</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">21</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 420px;"></div><div class="CodeMirror-gutters" style="height: 420px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 34px;"></div></div></div></div></pre><h2><a name="lock-%E9%94%81" class="md-header-anchor"></a><span>lock 锁</span></h2><p><span>lock 可以用来代替 synchronized 关键字，lock 接口有三个实现类 ReentrantLock（可重入锁）、ReetrantReadWriteLock.ReadLock（可重入读锁） 和 ReetrantReadWriteLock.WriteLock（可重入写锁）。</span></p><p><span>使用 synchronized 所有同步代码块都是互斥的，但是使用读写所的话，两个读锁不是互斥的，既然都是读取数据那也就没有互斥的必要。</span></p><p><span>lock 的优势有：</span></p><p><span>一、等待可中断，synchronized 等待不可中断</span><br/><span>这里的等待不是指对象调用 wait 方法后，线程进入对象的等待池，而是指线程在锁池内等待其他线程释放锁。</span><br/><span>可以调用lock 对象的 </span><code>lockInterruptibly()</code><span> 方法获取可中断的锁。如果某个对象中的同步代码块获得的锁是可中断的，有线程在执行该对象的同步代码块时没有获取锁，那该线程将等待背的线程释放锁，此时其他线程可以调用那个正在等待的线程（也就是 thread 对象）的 </span><code>interrupt()</code><span> 方法来中断它的等待，该线程将放弃执行同步代码块，继续执行下面的代码。</span></p><p><span>二、 可以实现公平锁</span><br/><span>创建锁时传入 true 参数，</span><code>new ReentrantLock(ture)</code><span>。线程在竞争同一个锁时按照申请时间排队等待。</span></p><p><span>三、同一个锁可以绑定多可条件</span><br/><code>Condition condition = lock.newCondition()</code><span>，condition 对象可以使用 </span><code>await(), signal(), signalAll()</code><span> 方法，效果同 object 的 </span><code>wait(), notify(), notifyAll()</code><span>，当然，只能由同一个。condition 对象的 signal 去唤醒 同一个 condition 对象的 await，lock 对象可以创建多个 condition 对象。</span></p><p><span>使用 lock 时一般采取如下写法：</span></p><pre spellcheck="false" class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 34px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>15</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -34px; width: 34px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">Lock</span> <span class="cm-variable">lock</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">ReentrantLock</span>();</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">Condition</span> <span class="cm-variable">condition1</span> <span class="cm-operator">=</span> <span class="cm-variable">lock</span>.<span class="cm-variable">newCondition</span>(); &nbsp;</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">3</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">.........</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">4</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">lock</span>.<span class="cm-variable">lock</span>(); &nbsp;</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">5</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">try</span> { &nbsp;</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">6</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp;  ......</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">7</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-comment">//只有当其他线程调用 condition1 的 signal 方法时才会被唤醒</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">8</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-comment">//调用其他 condition 对象的 signal 方法不会影响到它</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">9</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-variable">condition1</span>.<span class="cm-variable">await</span>()</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">10</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp;  ......</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">11</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-comment">//如果有 return 语句，放在这里 &nbsp;</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">12</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">finally</span> { &nbsp;</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">13</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-comment">//finally 保证锁一定会被释放</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">14</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-variable">lock</span>.<span class="cm-variable">unlock</span>();</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">15</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 300px;"></div><div class="CodeMirror-gutters" style="height: 300px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 34px;"></div></div></div></div></pre><h2><a name="%E7%BA%BF%E7%A8%8B%E4%BB%BB%E5%8A%A1-runnable-%E5%92%8C-callable" class="md-header-anchor"></a><span>线程任务 Runnable 和 Callable</span></h2><p><a href='http://blog.csdn.net/bboyfeiyu/article/details/24851847'><span>Java中的Runnable、Callable、Future、FutureTask的区别与示例</span></a></p><ul><li><strong><span>Runnable</span></strong><span>：无返回值，无法抛出异常，仅仅需要实现一个run方法</span></li><li><strong><span>Callable</span></strong><span>：和Runnable差不多，仅仅需要实现一个call方法，有返回值，能抛出异常。一般被ExecutorService执行</span></li><li><strong><span>Future</span></strong><span>：代表Runnable或者Callable任务的执行结果，可以用来取得Callable的返回值，取消任务的执行，判断任务是否被取消，判断任务是否执行结束。ExecutorService的submit方法可以返回Future对象</span></li><li><strong><span>FutureTask</span></strong><span>：实现Runnable和Future接口，同时构造器可以接受Runnable对象或者Callable对象。它可以被Thread和ExecutorService执行</span></li></ul><p><span>Future的get方法可获得运行的返回值，当get方法被调用时，当前线程被阻塞，直至Callable的call方法执行完毕并返回</span></p><h2><a name="thread" class="md-header-anchor"></a><span>Thread</span></h2><h3><a name="%E7%BA%BF%E7%A8%8B%E7%9A%84%E5%85%AD%E7%A7%8D%E7%8A%B6%E6%80%81" class="md-header-anchor"></a><span>线程的六种状态</span></h3><ul><li><strong><span>NEW</span></strong><span>：线程被创建但是还没有启动</span></li><li><strong><span>RUNNABLE</span></strong><span>：线程可运行（条件具备，就差 CPU），或者线程正在运行</span></li><li><strong><span>BLOCKED</span></strong><span>：阻塞，正在等待其他线程释放锁</span></li><li><strong><span>WAITING</span></strong><span>：正在等待其他线程唤醒它</span></li><li><strong><span>TIMED_WAITING</span></strong><span>：定时等待，到达时间后，即使没有被其他线程唤醒，也将自己醒来</span></li><li><strong><span>TERMINATED</span></strong><span>：终止</span></li></ul><p><span>进程的状态</span></p><ul><li><strong><span>就绪</span></strong><span>：条件具备，就差 CPU</span></li><li><strong><span>运行</span></strong></li><li><strong><span>阻塞</span></strong></li><li><strong><span>挂起</span></strong><span>：进程挂起后进入【就绪】状态</span></li></ul><h3><a name="%E7%BA%BF%E7%A8%8B%E4%B8%AD%E6%96%AD" class="md-header-anchor"></a><span>线程中断</span></h3><p><span>thread 对象的 </span><code>interrupt</code><span> 方法可以用来中断该线程，其实只是个给线程设置一个标志位，对线程的执行没有影响。</span><br/><code>isInterrupted</code><span> 方法判断线程有没有设置中断标志位。</span><br/><code>interrupted</code><span> 方法判断该线程有没有设置中断标志位，判断过后清除中断标志位。</span></p><p><span>任何能抛出 InterruptedException 异常的方法都能被中断，比如可以用 interrupt 中断线程的 sleep，sleep 被中断的话，中断标志位也会被清除。</span></p><p><span>手动中断线程可以这么做</span></p><pre spellcheck="false" class="md-fences md-end-block md-fences-with-lineno ty-contain-cm modeLoaded" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 38px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 34px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre><div class="CodeMirror-linenumber CodeMirror-gutter-elt"><div>14</div></div></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: -34px; width: 34px;"></div><div class="CodeMirror-gutter-wrapper CodeMirror-activeline-gutter" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">1</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">Thread</span> <span class="cm-variable">threadA</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">Thread</span>(){</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">2</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-meta">@Override</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">3</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp;<span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">4</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-keyword">super</span>.<span class="cm-variable">run</span>();</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">5</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-keyword">for</span> (<span class="cm-variable-3">int</span> <span class="cm-variable">i</span> <span class="cm-operator">=</span> <span class="cm-number">0</span>; <span class="cm-variable">i</span> <span class="cm-operator">&lt;</span> <span class="cm-number">999999999</span>; <span class="cm-variable">i</span><span class="cm-operator">++</span>) {</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">6</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-keyword">if</span>(<span class="cm-variable">interrupted</span>()){</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">7</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-comment">//中断新城不是终止线程，如果希望终止线程可以把这里的 break 改为 return</span></span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">8</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-keyword">break</span>;</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">9</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;  }</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">10</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">i</span>);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">11</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp;  }</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">12</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp; &nbsp; &nbsp; &nbsp;<span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"hello world"</span>);</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt" style="left: 0px; width: 26px;">13</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> &nbsp;  }</span></pre></div><div style="position: relative;"><div class="CodeMirror-gutter-wrapper" style="left: -34px;"><div class="CodeMirror-linenumber CodeMirror-gutter-elt CodeMirror-linenumber-show" style="left: 0px; width: 26px;">14</div></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">};</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom: 0px solid transparent; top: 280px;"></div><div class="CodeMirror-gutters" style="height: 280px;"><div class="CodeMirror-gutter CodeMirror-linenumbers" style="width: 34px;"></div></div></div></div></pre><p><code>join()</code><span>：用法示例：</span><code>threadA.join()</code><span>，当前线程将等待 threadA 线程执行完毕后继续执行。</span></p><h2><a name="%E7%BA%BF%E7%A8%8B%E6%B1%A0" class="md-header-anchor"></a><span>线程池</span></h2><p><a href='http://mangocool.com/1442994320089.html'><span>Executor线程池详解</span></a><span></span><br/><a href='http://www.jianshu.com/p/e317540a8313'><span>Android concurrent（一）—— Executor接口</span></a></p><p><span>线程池内有多个未死亡的线程（Thread对象），当一个任务需要用该线程池中的线程执行时，如果有线程处于等待状态，该任务就会被执行，如果所有线程都处于运行状态，则该任务在队列中等待有线程执行完毕。</span><br/><span>应该就是线程池内有一些 Thread 对象，然后可以把 Runnable 不断地传给 Thread 去执行。</span></p><ul><li><span>任务：需要执行的一系列操作，比如Runnable接口的对象</span></li><li><span>线程：任务的执行者，一个任务结束后，线程可以等待下一个任务，也可以被销毁</span></li></ul><blockquote><p><span>线程池的生命周期：运行（创建之后）、关闭（shutdown 方法被调用后）、终止</span>
<span>线程池必须要被 shutdown，否则的话它将一直等待新任务，程序会一直运行</span></p></blockquote><h3><a name="%E7%BA%BF%E7%A8%8B%E6%B1%A0%E7%9A%84%E5%87%A0%E4%B8%AA%E5%B8%B8%E7%94%A8%E7%B1%BB" class="md-header-anchor"></a><span>线程池的几个常用类</span></h3><ul><li><span>Executor：线程池的顶级接口、实际使用中很少用到</span></li><li><span>ExecutorService：真正会用到的线程池接口</span></li><li><span>Executors：线程池的工厂类，用来创建一些常用的线程池</span></li><li><span>ThreadPoolExecutor、ScheduledThreadPoolExecutor：用来自定义一些线程池</span></li></ul><p><code>Executor</code><span>（顶级接口）、</span><code>.*ExecutorService</code><span>（继承自顶级线程池的其他线程池接口、抽象类），</span><code>.*Executor</code><span>（线程池的具体实现类）</span></p><blockquote><p><span>JDK 文档强烈建议使用工厂类来创建常用的线程池对象，而不是手动 new</span></p></blockquote><h3><a name="%E5%88%9B%E5%BB%BA%E7%BA%BF%E7%A8%8B%E6%B1%A0" class="md-header-anchor"></a><span>创建线程池</span></h3><p><span>Executors（普通类）：包含几个静态方法，用来创建常用的线程池。这些方法返回的对象是ExecutorService（接口）类型的。</span></p><ul><li><span>newSingleThreadExecutor：永远只有一条线程在运行，也就是使用该线程池的任务都要排队。如果唯一的线程挂了，会自动创建一个新的线程</span></li><li><span>newFixedThreadPool：创建固定大小的线程池。每次提交一个任务就创建一个线程，直到线程达到线程池的最大大小</span></li><li><span>newFixedThreadPool：创建一个可缓存的线程池。如果线程池的大小超过了处理任务所需要的线程，那么就会回收部分空闲（60秒不执行任务）的线程</span></li><li><span>newScheduledThreadPool：创建一个大小无限的线程池。此线程池支持定时以及周期性执行任务的需求</span></li></ul><h4><a name="%E6%89%8B%E5%8A%A8-new-%E5%87%BA%E7%BA%BF%E7%A8%8B%E6%B1%A0" class="md-header-anchor"></a><span>手动 new 出线程池</span></h4><p><span>一般用ThreadPoolExecutor（普通类），它实现了ExecutorService接口，并且它有一个子类ScheduledThreadPoolExecutor</span></p><blockquote><p><span>ThreadPoolExecutor构造器的参数</span></p></blockquote><ul><li><span>int corePoolSize：池中所保存的线程数，包括空闲线程。</span></li><li><span>long maximumPoolSize：池中允许的最大线程数。</span></li><li><span>long keepAliveTime：当线程数大于核心时，此为终止前多余的空闲线程等待新任务的最长时间。</span></li><li><span>TimeUnit unit：keepAliveTime 参数的时间单位。</span></li><li><span>BlockingQueue workQueue：执行前用于保持任务的队列。此队列仅保持由 execute方法提交的 Runnable任务。</span></li><li><span>ThreadFactory threadFactory：执行程序创建新线程时使用的工厂。</span></li><li><span>RejectedExecutionHandler handler：由于超出线程范围和队列容量而使执行被阻塞时所使用的处理程序。</span></li></ul><blockquote><p><span>共有4个构造器，这些构造器所需的参数数量有5个到7个不等。好难，先不管</span></p></blockquote><h4><a name="executorservice-%E5%B8%B8%E7%94%A8%E6%96%B9%E6%B3%95" class="md-header-anchor"></a><span>ExecutorService 常用方法</span></h4><p><code>execute(Runnable)</code>
<code>abstract &lt;T&gt; Future&lt;T&gt; submit(Callable&lt;T&gt; task)</code><span>：与 execute 不同的是，它可以接收 callable 对象，也可以接收 runnable 对象，而且该方法有返回值</span>
<code>shutdown()</code><span>：停止接收新任务，等待正在运行的任务结束</span>
<code>shutdownNow()</code><span>：停止接收新任务，并中断（</span><code>Thread.interrupt()</code><span>）正在运行的任务。当然，线程如果不响应中断，那它还会继续执行</span>
<code>isShutdown()</code></p><h2><a name="%E5%85%B6%E4%BB%96%E7%9A%84%E5%A4%9A%E7%BA%BF%E7%A8%8B%E5%AE%9E%E7%8E%B0%E6%96%B9%E5%BC%8F" class="md-header-anchor"></a><span>其他的多线程实现方式</span></h2><h3><a name="timer-%E5%92%8C-timertask" class="md-header-anchor"></a><span>Timer 和 TimerTask</span></h3><p><span>Timer：英文意思是【定时器】，一个 Timer 对象就是一条线程。使用 schedule 方法启动线程（不是和 Thread 一样的start方法）。</span><br/><span>TimerTask：被 Timer 对象反复执行的任务，其内部的 run 方法需要被重写。</span><br/><span>这个两个类都有cancel方法，Timer 用该方法终止线程，该线程中所有 TimerTask 都不会被执行了，TimerTask 用它来把自己从Timer的线程中移除，但是 Timer 的线程不会终止，如果它还有其他 TimerTask，那么这些 TimerTask 依然会被执行。</span></p></div>
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